This invention relates generally to processes for manufacturing semiconductor integrated circuits.
In a variety of processes, metal lines may be formed. For example in conjunction with a damascene process, copper lines may be formed. Copper has many performance advantages over conventional aluminum interconnects.
Metallic copper a high tendency to become oxidized when exposed to strong acids or water at elevated temperatures. Copper forms oxides with difference oxidation states like Cu2O and CuO. Normally, hydrogen-plasma based cleans are used in the industry. But, more delicate dielectric materials (ILD) preclude the use of this technique due to the deleterious effect of the hydrogen plasma on the ILD properties and the dielectric constant of the ILD.
In the dual-damascene process, a copper line may exist at the bottom of a via trench through a dielectric material with a layer of metal oxide as a result of the cleans and other etch residue on its top surface. These copper oxides at the top of the exposed trench copper need to be removed or reduced back to metallic copper to form lower electrical resistance metal lines and connecting vias.
Thus, there is a need for better ways to clean metal lines and especially to clean metallic lines that are subject to oxide formation without damaging the properties of the delicate dielectric material.